Conventionally, rotation of a tire is detected by using a rotation detector designed for detecting the rotation of the tire as disclosed in Japanese patent document JP-A-2000-171475. The rotation detector as a tire speed sensor J1 detects a rotation angle of a tire by using a magnetic sensor such as Hall element, a rotating gear rotor J3 that represents rotation of a drive shaft J2, a magnet for magnetizing the rotor J3 and a processing circuit for processing an output signal from the magnetic sensor as shown in FIGS. 9A and 9B. The tire speed sensor J1 is disposed, for example, to oppose the gear rotor J3 fixed on the drive shaft J2 that drives the tire as shown in FIG. 9A.
The magnetism (direction of magnetic flux) from the magnet changes as teeth on the gear rotor J3 are driven by rotation of the gear shaft J2, because the teeth of the rotor J3 run through the magnetic flux that flows from the magnet toward the magnetic sensor. The change of the magnetic flux detected by the magnetic sensor is sent to the processing circuit as an output signal, and the output signal is converted to a pulse signal that represents a number of teeth that passed the magnetic flux. In this manner, the rotation of the tire is detected by using the pulse signal for use in, for example, a brake ECU or the like.
The tire speed sensor J1 has a wire J7 for outputting the pulse signal processed in the processing circuit, and the wire J7 extends in an axial direction (upwardly) from a sensor body J5 that houses the magnetic sensor, the magnet and the processing circuit for outputting as shown in FIG. 9A.
However, the wire J7 extending in the axial direction of the sensor body J5 interferes with a vehicle body or other parts disposed thereon because of a limitation of a space reserved for the sensor J1. That is, the wire J7 interferes, for example, with a suspension arm, a brake dust cover or the like.
In this case, the wire J7 of the sensor J1 has to be bent and extended perpendicularly against the axis of the sensor body J5 as shown in FIG. 9B.
Rotation speed of the tire is detected by using the same tire speed sensors J1 respectively disposed on both of the right side tire and the left side tire of a vehicle. However, the sensor J1 on the right side tire and the left side tire have to be in a different shape in spite of the symmetrical arrangement of the sensors J1 on the vehicle. This is because of the restriction on the arrangement of the magnetic sensor element against the rotation direction of the gear rotor J3. In other words, a stay for installation of the sensor J1 has different angles against the sensor body respectively for the sensor on the right side and the sensor on the left side.
FIGS. 10A and 10B shows illustrations of positional relationship between magnetic sensors J4 and the gear rotor J3. FIG. 11 shows a diagram that represents a relationship of a maximum amount of an air gap between the sensor body J5 and the gear rotor J3 against an arrangement angle of the sensors J4.
The magnetic sensors J4 are, for example, an arrangement of two Hall elements J4a, J4b. The sensor body J5 is disposed in such a manner that the arrangement of the two Hall elements J4a, J4b aligns with the rotation direction of the gear rotor J3. The rotation direction of the gear rotor J3 is perpendicular to a rotation axis in FIG. 10A.
The arrangement of the two Hall elements J4a, J4b may slightly be diverted from the rotation direction of the gear rotor J3 because of an assembly error or the like. The error of assembly in angle is expressed as θ, and the relationship between the error and the maximum air gap is shown in FIG. 11. As shown in the diagram in FIG. 11, the maximum air gap decreases as the error angle θ increases.
On the other hand, an air gap between the sensor body J5 and a top of the teeth of the gear rotor J3 must be greater than a predetermined value when a certain amount of the assembly error is expected in the course of assembly of the sensor body J5. Therefore, the predetermined value of the air gap defines a minimum amount of the air gap against a curve of the relationship between the maximum air gap and the error angle, thereby determining a range of the error angle θ.
FIG. 12A shows an illustration of a positional relationship between a stay J6 and the sensor body J5, and FIG. 12B shows an illustration of an arrangement of the tire speed sensor disposed on the right and left tires.
As shown in FIG. 12A, the stay J6 on the sensor body J5 has a certain angle against the arrangement of the two Hall elements J4a, J4b. That is, the stay J6 is not arranged perpendicularly to the two Hall elements J4a, J4b, but has a certain angle against the two Hall elements J4a, J4b. Further, the wire J7 extends toward an opposite side to the stay J6.
Therefore, the tire speed sensor J1 for use with a right tire is, for example, suitably used for the right tire as shown in FIG. 12A, that is, the arrangement of the two Hall elements J4a, J4b aligns with the rotation direction of the gear rotor J3 when the speed sensor J1 is disposed on a position that corresponds to the right tire. However, the same speed sensor J1 for use with a right tire cannot be suitably used for the left tire because of a restriction on the error angle. That is, the arrangement of the two Hall elements J4a, J4b does not fall within the range of the angle described above with reference to the diagram in FIG. 11 because the range of the error angle is very small on account of assembly error incorporated thereto.
As a result, the stay J6 of the tire speed sensor J1 has to have respectively different angles against the sensor body J5 for use with the right tire and with the left tire.
Japanese patent publication JP-A-2005-227177 discloses a tire speed sensor that has a perpendicularly bent body against the axis of the sensor body.
FIGS. 13A and 13B show illustrations of the speed sensor J1 disclosed in the application, and the wire J7 originally extends straight from the sensor body J5 as shown in FIG. 13A. The wire J7 is bent perpendicularly to the axis of the sensor body J5 in FIG. 13B.
The sensor body J5 has a plurality of a convex portions J5a on an outer periphery as shown in FIG. 13A, and an attachment J8 bends the wire J7 perpendicularly against the sensor body J5 when it is disposed on the sensor body J5 as shown in FIG. 13B. Further, the attachment J8 determines an extending direction of the wire J7 around the axis of the sensor body J5 when the attachment J8 is disposed on the sensor body J5 in association with one of a plurality of the convex portion J5a. In this manner, the speed sensor J1 in the disclosure is designed respectively for use with the right tire and for use with the left tire.
However, the attachment J8 increases the number of parts used to construct the speed sensor J1, and also increases the number of assembly processes and inspection processes to assure fixation of the attachment J8. Further, the attachment J8 is prone to falling-off from the sensor body J5 as well as breakage because of a resistance of the wire J7 against a bending force from the attachment J8. Furthermore, the attachment J8 has to have a certain strength to counter the resistance from the wire J7.
FIGS. 14A and 14B show illustrations of the tire speed sensor J11 having a different structure.
In this case, the wire J13 extends perpendicularly against the axis of the sensor body J12 by using an insert resin molding J14.
However, the insert resin molding J14 increases the number of parts to construct the speed sensor J11, and also adds an assembly process for installing the wire J3 into the insert resin molding J14. Further, the insert resin molding J14 has to be held during a sensor body molding process in order to avoid a defect in molding the sensor body J12 because pressure of molding that tilts the insert resin molding J14 results in an exposure of the insert resin molding J14. Furthermore, tilt of the insert resin molding J14 is prevented by using an insertion anchor pin J16 as shown in FIG. 14B. That is, a hole of the insertion anchor pin J16 left after pulling out the anchor pin J16 has to be mended either by a filling process after the molding or by a heating process in a step for pulling out the anchor pin J16. Therefore, the insert resin molding J14 also results in an increased number of manufacturing processes and a complicated procedure of assembly and the like.